1. Field of the Invention
The present invention relates to a scanning-member-stop positioning device, controlling the degree of the brake power against a scanning member consisting of an optical section or a document glass plate so as to stop it exactly at the home position, for the image forming apparatus like a copying machine, a document reader, and so on.
2. Description of the Prior Art
A copying machine will be illustrated in FIG. 6 as an example in the background of the invention. Said copying machine scans a paper on a document glass plate 2 with the exposure on account of movement of the optical section 1 comprising a light source etc. on right and left. While such a exposure scanning can be done by a movement of the document glass plate 2 under condition of stopping the optical section 1. Accordingly, the optical section 1 or the document glass plate 2 should be called "a scanning member" generally in the present invention.
A copying machine A shown in FIG. 6 is a type of having a movable optical section 1 waiting before a copying operation at the left end in the figure, namely a home position denoted by a reference sign 1a in FIG. 6.
In being pushed a print key at the time of the copying operation, the optical section 1 will start moving in the right direction in FIG. 6. When the optical section 1 passes over a read starting position 1b illustrated with the dotted line, a detect piece 1' installed in the optical section 1 actuates a read starting positional sensor SW.sub.1. The signal from said sensor SW.sub.1 determines the start timing of rotating a resisting roller 4 which conveys a paper 8 to a photoreceiptor drum 3. The optical section 1, which passes over the read starting position 1b, moves up to a position (the maximum movement up to a position 1c) in proportion to the document sizes to be lighted out. After that, the optical section goes back to the home position 1a. Then the optical section 1 goes back and forth in the number of times being equal to the copy quantity between the home position 1a and the end position at the right end in FIG. 6 (such as a position 1c) so as to scan the document with the exposure. The toner image formed on the surface of the photoreceiptor drums 3 is transferred on the paper 8 sent out by the resisting roller 4, and is fixed by a fixing roller 5. After that, the paper 8 is conveyed out on a copy tray 6.
The scanning member consisting of the above-mentioned optical section 1 or the document glass plate 2 in itself comprises some heavy parts such as the light source and its frame. Therefore the scanning member and the casing main body of the copying machine are deteriorated their durability by a gross load originated in a sudden stop of the scanning member at the home position 1a. For the purpose of copying with the foregoings, the back-running scanning member is relieved its stop shock by the stepwise brake operation generally, said scanning member is decelerated at the timing of passage over the read starting position 1b further is braked more powerfully for the purpose of its stop at the home position 1a. And these arts should be referred to J.P. (KOKAI) No. 62-129837 and to J.P. (KOKAI) No. 60-62776.
As described above, the stopping method of the scanning member by the stepwise brake operation is superior to the suddenly stopping one with regard to the point relieving the shock. And it is commonly known that the required degree of the brake power should change with frictional registance arising from a movement of the scanning member, the environment of a room temperature etc., the historical factor and so on. In spite of the foregoing description, an adjustment of said degree of the brake power is not so much correct in the prior art.